The following definitions of abbreviations will be useful in understanding the description presented herein:    DC Dual Connectivity    DL Down Link    DRB Data Radio Bearer    eNB E-UTRAN Node B    E-UTRAN Evolved UTRAN    HFN Hyper Frame Number    MeNB Master eNB    MAC Medium Access Control    RRC Radio Resource Control    SCG Secondary Cell Group    SeNB Secondary eNB    SN Sequence number    UE User Equipment    UL Uplink    UTRAN Universal Terrestrial Radio Access Network
One important development in efficient use of frequencies is dual connectivity. A wireless network can comprise large cells, also referred to as macro cells, defined as the service area of larger, higher-powered base stations. In 3GPP, 3GPP LTE, and 3GPP LTE-A networks and present and anticipated extensions and enhancements of such networks, base stations are referred to as enhanced Node Bs, (eNodeBs or eNBs) and the user devices served by the eNBs are referred to as user equipments or UEs.
In addition to large cells, a network may also comprise small cells operating within each of one or more large cells with a small cell being defined as the service area of a smaller, lower-powered eNBs. The large eNBs may be referred to as master eNBs or MeNBs, and the small eNBs may be referred to as secondary eNBs or SeNBs, with the SeNBs belonging to a secondary cell group (SCG). The frequencies used by SeNBs may be re-used within a large cell, because the small base stations have shorter ranges than do the larger base stations. Such dual connectivity using MeNBs and SeNBs comprises two different alternative architectures as defined by current 3GPP standards—architecture 1A and architecture 3C. In architecture 1A, a data radio bearer (DRB) is connected to the core network directly from the SeNB, and is called a secondary cell group (SCG) bearer. A bearer that is configured only via the MeNB is called a master cell group (MCG) bearer.
When there is no activity on a DRB, maintaining the bearer is an inefficient use of frequencies and of UE power, and if only one DRB is configured for a UE, maintaining the radio resource control connection for this DRB with no activity is also inefficient. Thus, an eNB usually releases its DRB when there is no traffic. In conventional approaches, this is accomplished with an implementation specific timer—if there is no data on the uplink or downlink for a specified time, the DRB, along with the RRC connection if there is only one DRB, is released.